Some embodiments described herein relate generally to the methods and apparatus for using information related to power harvesting conditions to alter the power-on sequence or boot sequence of an integrated circuit such as a system-on-chip (SoC).
Portable systems that operate from a battery and/or from power harvested from the environment typically consume small amounts of energy to prolong the system lifetime for a given amount of available energy. The energy budget for a portable system affects a widening set of applications due to a combination of design criteria for smaller size (less battery volume, so less energy available), longer lifetimes (make energy last longer), and/or more functionality (do more with the same amount of energy). An emerging class of these portable systems can be used as wireless nodes in a variety of applications, including providing monitoring, sensing, control, or security functions. An increasing fraction of attention to these sorts of devices, often classified as belonging to the emerging “Internet of Things (IoT)”, considers that they will typically operate at least in part using power harvested from their environment, and a new class of power harvesting systems on chip (SoCs) has emerged for this purpose. These SoCs may include combinations of power harvesting circuits, power management circuits, sensors or sensor interfaces, processing components (e.g. microcontrollers, microprocessors, digital signal processors, hardware accelerators), memory, and wireless communication circuits (e.g. radios).
SoCs with embedded processing elements typically follow a startup sequence that governs how they turn on and configure different components in the system and how the processors themselves boot into an operational state. The startup sequence is usually governed by hardware with some degree of programmability using software. The boot sequence of the processor usually executes code in a read only memory (ROM) (other options in place of the ROM include one-time programmable memory (OTP), multiple-time programmable memory (MTP), programmable ROM (PROM), electrically erasable PROM (EEPROM), and other various types of non-volatile memory (NVM)). The code in the ROM provides a way for the application that will eventually run on the processor to initialize itself and start executing. This boot sequence often includes the initialization of interrupt handlers or exception vectors, initialization of the stack, initialization of the memory system and of registers, peripheral initialization, configuration of I/O devices, security handling, interrupt enabling, processor mode configuration, variable initialization, (if no application code is available) boot loading of application code from an external source, and finally, jumping to the main application code.
The variable conditions inherent to power harvesting systems may result in situations in which the conventional methods for booting an integrated circuit such as an SoC significantly degrade the system's ability to provide reliable or long term functionality. Thus, a need exists for methods and implementations that allow energy harvesting systems to boot reliably across a range of power harvesting conditions.